rtant in the light which it may
throw on the scheme of the whole, and each fact is to be considered in
this light. As an instance: his discovery of the variable star
_[alpha] Herculis_, which has a period of sixty days, was valuable in
itself as adding one more to the number of those strange suns whose
light is now brighter, now fainter, in a regular and periodic order.
But the chief value of the discovery was that now we had an instance of
a periodic star which went through all its phases in sixty days, and
connected, as it were, the stars of short periods (three to seven days)
with those of very long ones (three hundred to five hundred days), which
two groups had, until then, been the only ones known. In the same way
all his researches on the parallaxes of stars were not alone for the
discovery of the distance of any one or two single stars, but to gain a
unit of celestial measure, by means of which the depths of space might
be sounded.

Astronomy in HERSCHEL'S day considered the bodies of the solar system as
separated from each other by distances, and as filling a cubical space.
The ideas of near and far, of up and down, were preserved, in regard to
them, by common astronomical terms. But the vast number of stars seemed
to be thought of, as they appear in fact to exist, lying on the surface
of a hollow sphere. The immediate followers of BRADLEY used these fixed
stars as points of reference by which the motions within the solar
system could be determined, or, like LACAILLE and LALANDE, gathered
those immense catalogues of their positions which are so indispensable
to the science. MICHELL and HERSCHEL alone, in England, occupied their
thoughts with the nature and construction of the heavens--the one in his
study, the other through observation.[34] They were concerned with all
three of the dimensions of space.

In his memoir of 1784, HERSCHEL says:

"Hitherto the sidereal heavens have, not inadequately for the
purpose designed, been represented by the concave surface of a
sphere, in the centre of which the eye of an observer might be
supposed to be placed.

"It is true the various magnitudes of the fixed stars even then
plainly suggested to us, and would have better suited, the idea of
an expanded firmament of three dimensions; but the observations upon
which I am now going to enter still farther illustrate and enforce
the necessity of considering the heavens in this point of view